Gases and liquids may be exchanged between a porous material and the surrounding atmosphere. Different types of sealing techniques or surface layers may be used for influencing the exchange of gas. Surface layers may also have other functions, such as protecting the material from disintegration and/or corrosion and for giving it an esthetically pleasing appearance.
Different types of surface layers may be used, such as paints or plastic films. Paints may be applied to wood surfaces and to different fibre based or synthetic construction materials. Plastic films may be used for packaging products that are to be protected from diffusion of oxygen, nitrogen or water, such as meat products, beverages, vegetables, etc. The object may be to prevent oxygen of the air from reaching the product or the material, or water or water vapour from penetration the material.
Handling of moisture in the construction of buildings may be a problem. Moreover, enclosed gases may be prevented from diffusion, such as for retaining the moisture and preventing drying.
Thus, there is a need for being able to determine the penetration properties of gases and liquids through surface layers for analysis and for the development of better properties of such surface layers.
A method of measuring properties of a material, such as gas contents, is presented in a publication by M. Sjöholm, G. Somesfalean, J. Alnis, S. Andersson-Engels, S. Svanberg: “Analysis of gas dispersed in scattering media”, Optics Letters Vol. 26, No. 1, Jan. 1, 2001, pages 16-18. It is mentioned that it would be possible by the technique disclosed therein to monitor in situ physiological and degradation processes in various biological substances. Moreover, dynamic processes may be monitored. Successive gas penetration into an object may be studied.
The method described in said publication is called the GASMAS (GAs in Scattering Media Absorption Spectroscopy) method and permits analysis of free gas in porous media. The important aspect is that the gas has extremely sharp absorption maximum compared to the surrounding material. By means of a narrow band laser and signal enhancement modulation techniques, enclosed gas penetrated by the input light can be monitored and appears as characteristic signals in the diffuse scattered light leaving the material. A demonstrated application is for ordinary oxygen which has been shown to appear in for example wood, frigolite and fruits.
Related technologies are described in EP-0768525 and U.S. Pat. No. 4,676,642.